of the Oxides of Manganese. 157 



verted into a red oxide containing but a very small proportion of 

 the deutoxide. It will appear from these experiments that it is 

 unsafe in analyses to heat the precipitated protoxide or carbo- 

 nate to redness, and consider the product as the deutoxide ; a 

 practice which is calculated to lead analytical chemists into 

 considerable errors, and indeed has actually done so. If it is 

 wished to procure the deutoxide, the precipitate should be moist- 

 ened with nitric acid, and then exposed to heat. 



I have endeavoured to ascertain the composition of the red 

 oxide by several methods. The first is by the combined agency 

 of heat and hydrogen gas. In the first experiments 100 parts 

 of pure red oxide, in being thus converted into the protoxide, 

 lost 6.802 and 6.817 parts of oxygen ; but as the resulting green 

 oxide, when put into dilute sulphuric acid, was found to contain 

 a little red oxide, the loss in oxygen must be rather below the 

 truth. To avoid this error I exposed 44.256 grains of red oxide 

 to hydrogen gas and a white heat for the space of one hour, 

 when the loss amounted to 3.153 grains on 7.125 per cent. 



Judging by the increase in weight which the protoxide ac- 

 quires when heated in the open air, 100 parts of the red oxide 

 consist of 93.05 parts of protoxide and 6.95 of oxygen. Accord- 

 ing to a similar experiment made by ARFWEDSON, the red oxide 

 is composed of 93.153 protoxide and 6.847 parts of oxygen. 



In an analysis already described, the carbonate of manganese 

 was found to contain 56.853 per cent of the protoxide of man- 

 ganese. When 100 parts of the same carbonate are exposed to 

 air and a white heat, 61.18 parts of red oxide are obtained. 

 From these data it may easily be calculated that the red oxide 

 consists of 92.927 parts of protoxide, and 7.073 of oxygen. 



As a mean of the numbers afforded by these three methods, 

 it follows that the red oxide is composed of 92.951 parts of the 

 green oxide and 7.049 of oxygen, or of 72.291 parts of metallic 



